Line wrenches are designed to operate on fasteners that are fitted to an elongate member, such as a pipe, electric cable or the like. For example, line wrenches are used to operate flare nuts that are fitted on fuel and hydraulic pipes and serve to secure the pipe to a metering unit of a fuel injection system or a hydraulic unit such as a hydraulic valve block or brake unit.
The obstruction provided by the elongate member makes it impossible to engage a fastener fitted on the member using a conventional box wrench, socket wrench or ring wrench. Conventional open-ended wrenches and crowfoot wrenches (see U.S. Pat. No. 2,600,617 or U.S. Pat. No. 6,805,029) can be used on such fasteners. However, they will usually only engage two surfaces of the fastener and so are prone to slippage when a large amount of torque needs to be applied. This can result in damage to the fastener, most likely rounding of the drive receiving surfaces and such damage can make it impossible to operate the fastener with an open-ended wrench. This is a problem often encountered when operating the flare nuts used to secure brake lines to brake units in automobile braking systems.
One known form of line wrench comprises a handle with a fixed socket head at one end. The socket head has a conventional hexagonal fastener receiving aperture, except that a side opening generally opposite the handle so that the fastener engaging faces of the fastener receiving aperture opposite the handle do not meet. Unlike an open ended wrench or crowfoot wrench, the side opening a line wrench has a width less than the across flats width of the fastener engaging aperture. Thus, the line wrench cannot be fitted directly onto a fastener by passing the fastener through the side opening and into the fastener receiving aperture. Instead, the line wrench is fitted over the fastener by first moving the wrench transversely of the elongate member associated with the fastener such that the elongate member passes through the side opening. The line wrench is then moved generally axially along the elongate member so that the fastener enters the fastener receiving aperture with its axis of rotation generally in line with the axis of the fastener receiving aperture. This conventional line wrench can be considered a hybrid of a conventional ring wrench and open ended wrench.
In common with other forms of wrench that have a side opening, these conventional line wrenches may spread when heavily loaded, leading to slippage and damage to the fastener. Also, because they need to be a stiff as possible so as to reduce the likelihood of spreading and must be made to exactly fit a particular size of fastener, for workshops and the like it is necessary to keep many different sizes of line wrench to fit the various sizes of fastener that may need to be operated. A further disadvantage of these known line wrenches is that they may be difficult, or impossible, to use in confined spaces or where a plurality of fasteners are grouped close together as, for example, on a metering unit of a fuel injection system.